LTC3406B-1.8 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC3406B-1.8' PDF : 16 Pages View PDF
LTC3406B
APPLICATIO S I FOR ATIO
1
RUN
5
VFB
LTC3406B
R2
2
–
GND
VOUT
+
COUT
L1
3 SW
4
VIN
CIN
BOLD LINES INDICATE HIGH CURRENT PATHS
R1
CFWD
+
VIN
–
3406B F05a
Figure 5a. LTC3406B Layout Diagram
VIA TO GND
1
RUN
–
VOUT
+
COUT
L1
LTC3406B-1.8
2
5
GND VOUT
3 SW
4
VIN
CIN
VIN
3406B F05b
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 5b. LTC3406B-1.8 Layout Diagram
VOUT
PIN 1
L1 SW
VIA TO VIN
LTC3406B
R1
R2
CFWD
COUT
CIN
GND
Figure 6a. LTC3406B Suggested Layout
VIN
VIA TO VOUT
VOUT
VIA TO VOUT
VIN
VIA TO VIN
PIN 1
L1
SW
LTC3406B-1.8
3406B F06a
COUT
CIN
GND
3406B F06b
Figure 6b. LTC3406B-1.8 Suggested Layout
Design Example
As a design example, assume the LTC3406B is used in a
single lithium-ion battery-powered cellular phone
application. The VIN will be operating from a maximum of
4.2V down to about 2.7V. The load current requirement
is a maximum of 0.6A but most of the time it will be in
standby mode, requiring only 2mA. Efficiency at both low
and high load currents is important. Output voltage is
2.5V. With this information we can calculate L using
equation (1),
( )( ) L =
f
1
∆IL
VOUT
⎛⎝⎜1−
VOUT
VIN
⎞
⎠⎟
(3)
Substituting VOUT = 2.5V, VIN = 4.2V, ∆IL = 240mA and
f = 1.5MHz in equation (3) gives:
L
=
1.5MH2z.(52V40mA) ⎛⎝⎜1 −
2.5V ⎞
4.2V ⎠⎟
=
2.81µH
A 2.2µH inductor works well for this application. For best
efficiency choose a 720mA or greater inductor with less
than 0.2Ω series resistance.
CIN will require an RMS current rating of at least 0.3A ≅
ILOAD(MAX)/2 at temperature and COUT will require an ESR
of less than 0.25Ω. In most cases, a ceramic capacitor will
satisfy this requirement.
3406bfa
12
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